This invention relates to radio receivers and, more particularly, to a miniaturized radio receiver suitable for direct attachment to the human ear.
Since the development of the transistor, small hand held transistorized radio receivers have become commonplace. To permit listening in private, hand held transistorized radio receivers are often provided with an earphone attachment comprising a speaker button adapted to fit in the ear of the user and a cable that connects the speaker button to the radio receiver.
The use of transistors has enabled a marked reduction in the size and weight of radio receivers. To further reduce size and weight, transistorized radio receivers generally employ a ferrite core antenna. Conventional ferrite cores are made of ferrous ferrite, magnesium ferrite, and zinc ferrite. However, one of the limiting factors on the size and weight of a transistorized radio receiver remains the ferrite core. The effective permeability and the effective height of a ferrite core are directly related to its length to width ratio. Further, the Q and the signal strength of the radio receiver are directly related to the effective permeability and the cross-sectional area of the core. Thus, to obtain a sufficiently small band width and a sufficiently large signal strength for acceptable radio reception, the length, width, and height of the core are decisive.
In the past there have been attempts to construct radio receivers adapted to be worn directly over the human ear. These radio receivers have proved to be bulky and uncomfortable to wear, partially as a result of the relatively large size of the ferrite core antenna or added circuitry to compensate for the low gain antenna system. Attempts have been made to employ the body of the user as the antenna for a radio receiver adapted to be placed inside the ear cavity; this results in radio reception that is dependent upon the proximity and condition of the ground plane.